Effect of Colloids on the Thermal Conductivity of γ-Irradiated KCl

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Abstract
The influence of γ irradiation at 300 and 77 K on the thermal conductivity of KCl in the range 0.4–4 K has been investigated. The results have been interpreted on the basis of the scattering of phonons by localized defects of both the point and extended varieties. The analysis is consistent with a defect model proposed for irradiated KCl by Sonder et al. This model postulates the formation of interstitial chlorine atoms which aggregate to form (colloid) clusters whose size and number depend on the irradiation temperature of the crystal. Evidence of aggregates with an effective radius of 70 ± 5 Å has been found for three different single crystals (from two sources of supply) irradiated at 300 K. For a sample crystal irradiated at 77 K and measured after direct cooling to 4 K, there was a significantly larger decrease in conductivity suggesting the possibility of extended defects which disappear after a short annealing period at 300 K.